1. Field of the Invention
The present invention relates to a contactless power transmitting system and a contactless charging system.
2. Description of the Related Art
Conventional contactless charging systems (contactless power transmitting systems) for portable telephones do not have a high power transmission efficiency, since they are affected by leakage inductance.
In view of the foregoing, it is an object of the present invention to provide a contactless power transmitting system, having a power transmitting circuit and a power receiving circuit which are connected via a transformer, with improved power transmission efficiency.
Another object of the present invention is to provide a contactless charging system, having a power transmitting circuit and a power receiving circuit which are connected via a transformer, with improved power transmission efficiency.
Still another object of the present invention is to provide a contactless power transmitting system, having a power transmitting circuit and a power receiving circuit which are connected via a transformer, with improved power transmission efficiency, and with significantly decreased current flowing through the primary coil of the transformer and with significantly decreased voltage of the secondary coil of the transformer when no load is applied to the rectifier circuit of the power receiving circuit compared to those when a load is applied thereto.
Further object of the present invention is to provide a contactless charging system, having a power transmitting circuit and a power receiving circuit which are connected via a transformer, with improved power transmission efficiency, and with significantly decreased current flowing through the primary coil of the transformer and with significantly decreased voltage of the secondary coil of the transformer when no rechargeable battery is connected to the rectifier circuit of the power receiving circuit compared to those when the rechargeable battery is connected thereto.
In order to achieve these objects, according to a first aspect of the present invention, there is provided a contactless power transmitting system. The contactless power transmitting system includes a power transmitting circuit and a power receiving circuit which are coupled by a transformer having a primary coil and a secondary coil. The power transmitting circuit includes a switching power supply having a predetermined frequency. The power receiving circuit includes a capacitor which is connected to the secondary coil and which constitutes a resonating circuit in cooperation with the leakage inductance of the secondary coil; and a flyback rectifier circuit. The capacitance of the capacitor is set such that the resonant frequency of the resonating circuit is substantially equal to the predetermined frequency of the switching power supply.
According to a second aspect of the present invention, there is provided a contactless charging system. The contactless charging system includes a power transmitting circuit and a power receiving circuit which are coupled by a transformer having a primary coil and a secondary coil. The power transmitting circuit includes a switching power supply having a predetermined frequency. The power receiving circuit includes a capacitor which is connected to the secondary coil and which constitutes a resonating circuit in cooperation with the leakage inductance of the secondary coil; and a flyback rectifier circuit to be connected to a rechargeable battery. The capacitance of the capacitor is set such that the resonant frequency of the resonating circuit is substantially equal to the predetermined frequency of the switching power supply.
In the first aspect of the present invention, preferably, the turns ratio of the primary coil to the secondary coil of the transformer is set such that the difference between the resonant frequency of the resonating circuit when a load is connected to the rectifier circuit and the resonant frequency of the resonating circuit when the load is not connected thereto becomes large.
In the second aspect of the present invention, preferably, the turns ratio of the primary coil to the secondary coil of the transformer is set such that the difference between the resonant frequency of the resonating circuit when the rechargeable battery is connected to the rectifier circuit and the resonant frequency of the resonating circuit when the rechargeable battery is not connected thereto becomes large.